Glass fiber mat reinforced plastic panels without the fiber readout defect

ABSTRACT

A method of making glass fiber mat reinforced RIM panels wherein glass fibers are kept away at a distance from the panel surface in a precisely controlled manner to avoid fiber readout defect. The method is carried out by molding glass fiber mats in a matched metal mold where at least one of the interior mold surface is etched with equally spaced, closely packed minute pockets or valleys of truncated pyramid shape. Fiber glass mat reinforced panels thus produced have a textured panel surface with a multiplicity of minute truncated pyramid like protuberances. Glass fibers are excluded from such protuberances to produce a panel surface without the fiber readout defect.

FIELD OF THE INVENTION

The present invention relates to a method of producing glass fiberreinforced plastic panels and, more particularly, relates to a method ofproducing a glass fiber mat reinforced plastic panel without the fiberreadout defect on the surface of the panel.

BACKGROUND OF THE INVENTION

Glass fiber reinforced plastics have been used widely in the automotiveindustry in recent years. These plastics include sheet molding compound,glass fiber reinforced reaction injection moldable materials and variousother glass fiber reinforced plastics. The advantages of lightweight,high strength, rust proofing and relatively low cost make thesematerials ideal for many automotive exterior body panel applications.

Of these materials, the reinforced reaction injection moldable material(RRIM) is of particular interest of the automotive industry because itcan be processed economically with relatively low cost tooling. RRIMmaterials filled with glass fiber mats have greatly improved stiffnessand dimensional stability and therefore are especially suitable for manyautomotive exterior body panel applications. The processing of suchglass fiber mat reinforced RIM is relatively simple. The processinvolves placing a glass fiber mat in a mold cavity and injecting RIMmaterial into the closed mold such that the RIM material is soakedthrough the glass fiber mat. A completed plastic part can be removedafter it is cured in the mold.

A typical RIM material used in this process is a polyurethane basedmaterial produced from two components, an isocyanate and a polyol. Thein-mold pressure of such a material system used in A RIM process istypically less than 50 psi. As a consequence, low cost tooling havinglow clamping force can be used for the process.

The dimensional stability of glass fiber mat reinforced RIM material isgreatly improved over that of a RIM material reinforced with milledglass. As a matter of fact, the dimensional stability of glass fiber matreinforced RIM is even superior to that of aluminum. This superiordimensional stability is achieved while other traditional benefits ofRRIM, i.e., stiffness, strength, and ease of processing are maintained.

In the processing of glass fiber mat reinforced RIM materials, a newproblem was discovered. This is generally called a fiber readout defectobserved in the surface layer of a glass fiber mat reinforced RIM part.It is a particularly serious problem when panels are used for exteriorautomotive body applications where aesthetic quality is of primeimportance.

The fiber readout problem is caused largely by the presence of glassfiber in the surface layer of a plastic panel. When a panel is situatedin a mold under compression, resin material located between the panelsurface and a glass fiber in the surface layer of the panel is underhigher pressure than that located not adjacent to a glass fiber. As aconsequence, when the part is demolded, the cured resin material locatedadjacent to a glass fiber will expand more than the resin material notadjacent to a glass fiber. This results in a panel having a surfaceshowing protruding contours of glass fibers which are locatedimmediately below the surface of the panel, commonly known as the fiberreadout phenomenon.

Numerous efforts have been made to correct the fiber readout defectobserved in glass fiber mat reinforced plastic panels. These effortsinclude the inventor's previous U.S. patent application Ser. No.669,824, filed Nov. 9, 1984 and assigned to the assignee of thisinvention. In that application, the inventor has shown that theapplication of a top coating layer in a secondary moding process couldconceal fiber readout if pressure was released before the end of themolding cycle. However, this process requires delicate process controlwhich may not be feasible in a mass production process.

It is therefore an object of the present invention to provide a methodof producing glass fiber mat reinforced RIM panels without the fiberreadout defect which is readily adaptable to a mass production process.

It is another object of the present invention to provide a method ofmaking glass fiber mat reinforced RIM panels where glass fibers are keptaway at a distance from the surface in a precisely controlled manner toavoid fiber readout defect.

It is yet another object to the present invention to provide a method ofmaking glass fiber mat reinforced RIM panels without the fiber readoutdefect such that panels can be readily decorated to produce apredecorated surface for automotive exterior body panel applications.

SUMMARY OF THE INVENTION

I have recognized that the fiber readout defect is caused by those glassfibers which are entrapped in a layer of plastic material immediatelyadjacent to the surface of the panel. Therefore, I have devised a noveltechnique by which glass fibers are kept away from the surface plasticlayer at a distance during molding of such panels in a preciselycontrolled manner.

In accordance with a preferred practice of my invention, a method ofproducing glass fiber mat reinforced plastic panels without the fiberreadout defect can be carried out by the following operative steps.

First, a set of matched metal mold is prepared of which at least one ofthe two opposing interior mold surfaces is etched with equally spaced,closely packed minute pockets or valleys of truncated pyramid shape. Oneor more layers of glass fiber mats are then placed in the mold. Afterclosing the two halfs of the mold together, polyurethane resin isinjected into the mold cavity. A sufficient time is allowed for thepolyurethane to cure before the mold is opened. A fiber glass matreinforced plastic panel of textured surface having a multiplicity ofminute truncated pyramid like protuberances is thus produced. Glassfibers are excluded from the protuberances molded on the panel surfacein such a way that none of the fiber readout defect is shown on thesurface.

Optionally, a predecorated plastic panel can be obtained by laminating apredecorated plastic sheet to such a molded panel. The laminationprocess can be easily performed by first coating the molded panelsurface with a urethane type resin material and then vacuum forming apredecorated plastic sheet over it. The predecorated plastic sheet canbe either a prepainted sheet meeting class A finish requirements of theautomotive industry or an otherwise predecorated sheet. A finished panelproduced from this lamination process can be readily used as anautomotive exterior body panel without further painting or decorating.

DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent upon consideration of the specification and the appendeddrawings, in which:

FIG. 1 is an enlarged perspective view of an interior mold surfacehaving minute pockets of truncated pyramid shape.

FIG. 2 is an enlarged perspective view of a glass fiber mat reinforcedplastic panel having minute truncated pyramid shaped protuberancesproduced from a mold depicted in FIG. 1.

FIG. 3 shows an enlarged sectional view of the alternate embodiment of apredecorated panel where a predecorated plastic film is vacuum formedand laminated to the glass fiber mat reinforced plastic panel by firstcoating the panel surface with a urethane type resin.

DESCRIPTION OF THE PREFERRED EMBODIMENT

My invention is a unique technique which allows for the production ofglass fiber mat reinforced plastic panels without the fiber readoutdefect. The technique is to first make a mold surface having a pluralityof closely-packed upstanding projections defining a plurality offlat-bottomed valleys of truncated pyramid shapes therebetween. RMmaterial is then injected into the mold after glass fiber mats areplaced in the mold. The upstanding projections on the surface of themold contact the glass fiber mats in such a way that the mats aresubmerged inside the panel and kept away from the panel surface.

Glass fiber mat reinforced plastic panels thus produced have texturedsurfaces comprising a large number of closely packed truncated pyramids.The dimensions of the pyramids are carefully chosen such that glassfiber bundles in the glass fiber mat cannot enter the pyramids. Thisresults in a top surface of the plastic panel containing a large numberof truncated pyramids which are formed competely of the RIM materialwithout any content of fiber glass. In other words, all the fiber glassbundles are kept away from the surface of the plastic panel by adistance approximately equal to the height of the pyramid. A plasticpanel having a surface that does not contain any glass fiber bundles inthe surface layer immediately adjacent to the surface is thus produced.The profiles of the glass fibers are not reproduced on the surface ofthe panel after molding, i.e., the defect of fiber readout is avoided.

Referring initially to FIG. 1, an enlarged cut-away surface of a mold 10containing numerous valleys of truncated pyramid shape is shown. Thedimensions of valley 12 of truncated pyramid shape are carefully chosensuch that glass fiber bundles can not enter such valley. For instance,suitable dimensions for the pyramid are 0.4 mm of the base width 14 ofthe pyramid, 0.2 mm for the top width 16 of the pyramid; 0.25 mm for theheight 18 of the pyramid, and 0.05 mm for the upstanding projection orthe ridge 20 between the bases of the pyramids. These dimension werefound suitable for the glass fiber mat used in my invention which isM-8605 (density 0.04 g/cm²) supplied by Owens-Corning Glass Co. Ridge 20serves to push down the glass fiber mat during molding and keeps theglass fibers away from the panel surface. The technology of makingcontinuous glass fiber mats is well known today and can be found in manytechnical publications. For instance, it is described in theEncyclopedia of Polymer Science and Technology, Vol. 6, page 639. I havealso found that a suitable way of etching such valleys in the surface ofa metal mold is by the photographic method.

After a mold surface is prepared as that depicted in FIG. 1, the moldingoperation of the plastic panel can be performed. Glass fiber mats arefirst placed into the open mold and positioned. The two matched metalmolds are then closed together and a polyurethane resin material isinjected into the mold cavity. The upstanding projection or the ridge 20(FIG. 1) on the surface of mold 10 contacts the glass fiber mats in sucha way that the mats are submerged inside the panel and kept away fromthe panel surface. Injection molding of polyurethane type RIM resin isperformed by the standard practice used in the plastics industry. Thepolyurethane resin utilized in this invention is composed of twocomponents, an isocyanate and a polyol. The isocyanate was supplied bythe Upjohn Co. as Isonate 181 within an equivalent weight of 183.3. Thepolyol component NIAX 11-34 was supplied by Union Carbide Co. which hasan equivalent weight of 1516.2. An ethylene glycol chain extender wasused in the formulation which is supplied by Fisher Scientific as gradeAR. The catalyst used in this formulation was Formex UL-29 supplied bythe Whitco Chemical Co. An internal mold release agent was used to easeprocessing which was supplied by the Specialty Products Co. as theirKANTSTIK FX-7. The formulation of this polyurethane composition is shownin Table 1.

                  TABLE 1                                                         ______________________________________                                        Formulation of Polyurethane Resin                                             Component          Weight Percent                                             ______________________________________                                        Polyol (Niax 11-34)                                                                              50.0                                                       Isonate 181 (Upjohn)                                                                             44.0                                                       Ethylene Glycol    6.0                                                        (Fisher Scientific, grade AR)                                                 Internal Mold Release                                                                            0.2                                                        (Kantstik FX-7)                                                               Catalyst (Formez UL-29)                                                                          0.01                                                       ______________________________________                                    

After injection, the urethane panel is allowed to cure in the mold for 5minutes at 67° C. After the panel is demolded and cooled to roomtemperature, it showed a surface containing a very large number oftruncated pyramids. An enlarged sectional view of this surface is shownin FIG. 2. The top layer 30 of the plastic panel containing the pyramidsare shown in FIG. 2. Glass fiber bundles 32 were too large to entervalleys 12 (FIG. 1) and are thus kept away from pyramids 34. A panelsurface having truncated pyramids which do not contain any glass fibersis thus produced.

It must be noted that even though my preferred practice of buildingprotuberances on a plastic panel surface is described in terms oftruncated pyramids, the practice of this invention is by no meanslimited to only such shape. For instance, tapered cylindrical shapedpyramids or tapered triangular shaped pyramids or even non-taperedvariations of such shapes should work equally well. The criticalrequirement to be met here is that the dimensions of the protuberancesmust be chosen such that the glass fiber bundles contained in the fiberglass mat cannot enter the valleys during the molding process. In otherwords, the valleys must be filld completely by the resin material. Bykeeping the fibers at a distance from the surface of the panel, thedefect caused by fiber readout is avoided.

The plastic panels having a textured surface can be used as is, withoutfurther decorating or can be painted and used in automotive interiorapplications, such as seat backs and load floors. In an alternateembodiment which is more adaptable to automotive exterior body panelapplications, a predecorated plastic sheet or film can be laminated tothe plastic panel surface to make it a predecorated plastic panel. Athin layer of approximately 0.025 mm of the same urethane resin, butwithout the mold release additive, is brushed over the panel surface anda prepainted carrier film if vacuum formed against it. This is performedin a vacuum box where a preheated sheet (to approx. 67° C.) is stretchedin a frame and positioned over a plastic panel. Vacuum is applied by avacuum pump (28 in Hg vacuum) through the bottom side of the box whilethe plastic panel is being pushed up to meet the plastic sheet. Thevacuum forming cycle time was about 5 minutes. An enlargedcross-sectional view of a laminated panel is shown in FIG. 3.

FIG. 3 shows that a prepainted plastic film 40 is laminated to a plasticpanel 30 by a layer of urethane resin 42. The prepainted plastic sheet40 has a paint layer 50 sprayed on it prior to the lamination process togive it a finished appearance. A finish meeting the automotive class-Afinish standard without fiber readout defect can be obtained by thistechnique.

The use of prepainted plastic film eliminates the cost of painting afterlamination. However, if it is desired, unpainted films can be usedequally well to cover the panel surface and painting can be carried outin a subsequent process. This is possible because the distance betweenthe fibers and the panel surface can be adjusted by my novel techniquesuch that the part will not show fiber readout even after the bakingtemperature of the paint.

While my invention has been described in terms of a preferred embodimentthereof, it is to be appreciated that those skilled in the art willreadily apply these teachings to other possible variations of theinvention.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A reinforced plasticpanel comprising a mat of glass fibers inpregnated with a plasticmaterial, said panel having a textured surface formed concurrently withsaid panel and comprising a multiplicity of minute truncated pyramids ofsubstantially equal height, each of said pyramids being substantiallyfree of glass fibers and having a surface substantially parallel to theplane of said panel, whereby said surface of said pyramid defines theoutermost surface of said reinforced panel which is free of theattendant undesirable appearance otherwise resulting from the presenceof said fibers on said surface and is readily decorable in a subsequentprocess.
 2. A predecorated plastic panel comprising a predecoratedplastic sheet laminated by adhesive means to a substrate molded of glassfiber mat impregnated with plastic material, said substrate having atextured surface formed concurrently with said substrate and comprisinga multiplicity of minute truncated pyramids of substantially equalheight, each of said pyramids being substantially free of glass fibersand having a surface substantially parallel to the plane of saidsubstrate whereby said surface of said pyramid defines the outermostsurface of said substrate which is free of the attendant undesirableappearance otherwise resulting from the presence of said fibers on saidsubstrate surface.